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Trusting CID and picking a Bus Bar
#1
Hello, First post here and first project(of many).  I built a spot welder and ordered my chargers/testers.

I usually do IT work but I am have done light residential electrician work.

I am planning a 7s20p pack for back up power during outages(fridge etc) for my Mom and later they may buy an RV and this would be super useful with a simple addition of a charge controller and a few solar panels

I am using new batteries(although they are from aliexpress), they came in, got charged and are now sitting put away waiting for the passive discharge test, then I plan to capacity test them with the Lii-500S's and planning out balanced series.

The battery would power a 110vac inverter(1500/3000) and some bucks to 5v(3x2a) and 12v(10a).

Since my cells have CID, why would I try to fuse each individual cell? Is CID not trustworthy? I am leaning to forgo the individual fusing, alternetively I am considering spotwelding some thickness(width, and length) nickel strips to the bus bar.

Also what would be a reasonable bus bar design to handle ~60A for peak. I plan to have a breaker for 60A.

I was planning on using a doublewide nickel strip and then putting a bus bar on there of unknown size and material(2xAWG8 for easy into TX90? and plenty wiggleroom), the bus bars would go to a XT90 on both leads, so each Series would have a male and a female connector.

Please let me know if im missing some glaring issue.

batteries -ali

BMS -ali

math - google sheets
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#2
CIDs are NOT fuses. They are in case the cell overheats to the point of failure. A fuse is a safety feature against over-current in/out the cell. A CID is kind of like an Air Bag in a vehicle. Having an air bag doesn't negate the need to wear a seat belt, does it? Of course not.
One device tries to protect in the extreme whereas the other tries to protect under standard and less severe issues.
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#3
I really like the air bag / seatbelt analogy when comparing CID vs fuses.

That said, many commercial packs are not built with fuses, and depending on the application and how the pack was built, I would not fuse individual cells. For high drain applications, e-bikes, power tools, where packs are well constructed and protected, I would opt for traditional construction with spot welded nickel strips and fuse the battery pack as a whole.

Of course, you can do it how you like. You have the creative freedom as this is YOUR design.
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#4
The most useful function is saving user error. One user accidentally shorted a cell with solder, this destroyed the cell. But the fuses did save a catastrophe. This is definitely a good reason for me. If a metallic object shorts the positive top to the negative case, even a small number of parallel cells could heat that object up enough to cause that cell to catch fire. This is also why I would fuse both sides of a cell.

Given many are using second hand cells, it is well more than possible for a piece of stray debris to find its way where it shouldn't.

That alone is my only argument for fusing cells.
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#5
May I ask what cells you bought? If they where genuine new cells i would personally not fuse them in such a "small" pack. With that said Aliexpress is known to have 95% fakes Tongue

/Daniel
The Ultimate DIY Solar and build place
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#6
Also the fuses really don't add much cost or time at all on completing the packs, but the level of protection they give is well worth it. With a spot welder you may or may not be able to just weld the fuse legs directly onto the battery anode and then solder the other end to your busbar. If you can't (I understand you made your own spot welder and depending on what you used it may just be too difficult to dial in) then you could just cut a little bit of nickel strip, solder one fuse leg to the very end of the cut strip and then weld the other ends onto the battery. The latter instance does create an extra step in putting packs together but it's a very short step and, again, of time spent is well out weighed by the safety obtained.

I used the glass axial fuses but you could also just get fuse wire. Keep in mind the glass axial fuses tend to actually pop at about double their rating (2A fuses will go around 3.5 or 4A in reality). They're dirt cheap too when purchased from aliexpress. On eBay they are slightly more expensive but you also get them five times quicker.
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#7
(08-23-2019, 07:14 AM)OhmGrown Wrote: Also the fuses really don't add much cost or time at all on completing the packs, but the level of protection they give is well worth it. With a spot welder you may or may not be able to just weld the fuse legs directly onto the battery anode and then solder the other end to your busbar. If you can't (I understand you made your own spot welder and depending on what you used it may just be too difficult to dial in) then you could just cut a little bit of nickel strip, solder one fuse leg to the very end of the cut strip and then weld the other ends onto the battery. The latter instance does create an extra step in putting packs together but it's a very short step and, again, of time spent is well out weighed by the safety obtained.

I used the glass axial fuses but you could also just get fuse wire. Keep in mind the glass axial fuses tend to actually pop at about double their rating (2A fuses will go around 3.5 or 4A in reality). They're dirt cheap too when purchased from aliexpress. On eBay they are slightly more expensive but you also get them five times quicker.

I was thinking of using 5a, if i do, as my surge current should be about 2.5a per cell to lower the resistance a bit.  Knowing that they would not blow until 10a is concerning, im just gonna order a couple hundred of a few different ones as you said they are 1c a piece on alieexpress and try to burn some up.

EDIT:
The spotwelder i made is based on 330CCA 12v battery, starter solenoid(closing the -), a relay to fire the solenoid and an arduino. The welds i liked were about 15ms(Lowest I can go is 12ms for the solenoid to close) in the code, but i dont know think thats the real timing, but it is consistent.  

(08-23-2019, 06:06 AM)daromer Wrote: May I ask what cells you bought?  If they where genuine new cells i would personally not fuse them in such a "small" pack. With that said Aliexpress is known to have 95% fakes Tongue

/Daniel
I grabbed the Liitokala original 18650 3400mAh NCR18650B 3.7V battery from LiitoKala Official Flagship Store, they dont look very real (missing the authenticity sticker) and i dont think the store is official at all.

I did capacity test a few and they came back as 3450+.

out of the 134 that arrived(I got shorted 10, dispute in progress) I recall only 3-4 being lower voltage then the rest, I marked them and they are still all resting before the self discharge test. I am actually ok with that result, im just going to have to order a few more cell, as I dont think changing manufacturer is a good idea.

Next week, im gonna cap test them all and have more results.
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#8
Sounds fine then. Once again new cell i wouldnt fuse them in such small packs.

Fusing individuall cells are for when 1 cell short out due to for instance age or abuse since before. New cells dont have that and you will be able to controll it.
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The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#9
(08-23-2019, 01:08 PM)daromer Wrote: Sounds fine then. Once again new cell i wouldnt fuse them in such small packs.

Fusing individuall cells are for when 1 cell short out due to for instance age or abuse since before. New cells dont have that and you will be able to controll it.
what do you think the safest way to test the CID/its presence would be?
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#10
(08-27-2019, 12:04 PM)diib Wrote:
(08-23-2019, 01:08 PM)daromer Wrote: Sounds fine then. Once again new cell i wouldnt fuse them in such small packs.

Fusing individuall cells are for when 1 cell short out due to for instance age or abuse since before. New cells dont have that and you will be able to controll it.
what do you think the safest way to test the CID/its presence would be?

In order to test it, you pretty much destroy the cell.  Similar to an air bag, you have to trust it to do its job, but you can test it by running into something with your car until it deploys.
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